For example, although ammonia is an essential compound in agriculture and industry, it is hazardous to humans and hence there are various known methods for decomposing ammonia in water and the air. A method for removing ammonia through decomposition from water containing ammonia at a high concentration has been proposed: aqueous ammonia being sprayed is brought into contact with airflow to separate ammonia in the air and the ammonia is brought into contact with a hypobromous acid solution or sulfuric acid (Patent Literature 1). Other methods have also been proposed: ammonia is separated in the air by the same process as in the above-described method and the ammonia is incinerated with a catalyst (Patent Literature 2); and ammonia-containing wastewater is decomposed with a catalyst into nitrogen and water (Patent Literature 3). In general, waste gas from semiconductor fabrication equipment contains ammonia, hydrogen, and the like. To completely remove the odor of ammonia, the amount of ammonia needs to be reduced to the ppm order. For this purpose, a method has been commonly used in which waste gas to be released from semiconductor equipment is passed through scrubbers so that water containing chemicals absorbs the hazardous gas. On the other hand, in order to decompose a hazardous gas at a low running cost without supply of energy, chemicals, or the like, a treatment method for waste gas from semiconductor fabrication equipment or the like has also been proposed: ammonia is decomposed with a phosphoric acid fuel cell (Patent Literature 4).